1. Field of the Invention
A impact tool such as a stapler, nailer or the like has a continuously running motor and a driven member such as a gear coupleable to a reciprocal drive bar in a power stroke for driving fasteners at a maximum rate of not more than once for every two rotary cycles of the gear. When fastening is not desired the motor will remain on but the drive bar will not partake of a power stroke. In the preferred embodiment a drive pin is included in and controlled via an interrupt means selectively to couple and uncouple the drive bar and the driven member. The drive bar partakes of a power stroke and a return stroke, and will be positively driven to cycle from a start position in which it receives or releases the pin during a predetermined dwell angle.
The interrupt mechanism also includes a track and shifter moveable to control the drive pin responsive to an arming linkage which senses the existence of system parameters such as workpiece engagement and operator actuation of the tool.
2. Description of the Prior Art
Fastening tools of the prior art used various power sources such as electric or pneumatic motors, compression springs and the like, to power a ram or other impact member in a positive manner, but such devices had a drive or return stroke which relied on the stored energy in: (1) the system; (2) the impact member; or (3) a drive or return spring. Pairs of flywheels, motor driven, were also used as a power source to drive a ram, but as noted above though the drive was positive, the return was not. Some prior art fastener tools were powered by a solenoid. In any event, all prior art fastener tools were believed to have one or more disadvantages as follows: complex; heavy; hard to control; unstable; and/or expensive.
Another feature found in the prior art is in the nature of a direct drive wherein the motor is mechanically coupled directly to the impact member so that power strokes are on a one-to-one basis with the cycles of operation of the motor. Accordingly, the fastener tool's motor had to have sufficient energy to drive the fasteners.
Examples of various prior art patents may be found as follows: Motor powered--U.S. Pat. Nos. 1,823,644; 1,845,617 (remote motor); Solenoid powered--U.S. Pat. No. 3,169,559; Pair of flywheels--motor powered--U.S. Pat. Nos. 4,204,622; 4,121,745; 4,042,036.